Dynamic size of static SLC cache

ABSTRACT

Apparatus and methods are disclosed, including using a memory controller to track a maximum logical saturation over the lifespan of the memory device, where logical saturation is the percentage of capacity of the memory device written with data. A portion of a pool of memory cells of the memory device is reallocated from single level cell (SLC) static cache to SLC dynamic cache storage based at least in part on a value of the maximum logical saturation, the reallocating including writing at least one electrical state to a register, in some examples.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No. 16/510,526, filed Jul. 12, 2019, which is incorporated herein by reference in its entirety.

BACKGROUND

Memory devices are semiconductor circuits that provide electronic storage of data for a host system (e.g., a computer or other electronic device). Memory devices may be volatile or non-volatile. Volatile memory requires power to maintain data, and includes devices such as random-access memory (RAM), static random-access memory (SRAM), dynamic random-access memory (DRAM), or synchronous dynamic random-access memory (SDRAM), among others. Non-volatile memory can retain stored data when not powered, and includes devices such as flash memory, read-only memory (ROM), electrically erasable programmable ROM (EEPROM), erasable programmable ROM (EPROM), resistance variable memory, such as phase change random access memory (PCRAM), resistive random-access memory (RRAM), or magnetoresistive random access memory (MRAM), among others.

Host systems typically include a host processor, a first amount of main memory (e.g., often volatile memory, such as DRAM) to support the host processor, and one or more storage systems (e.g., often non-volatile memory, such as flash memory) that provide additional storage to retain data in addition to or separate from the main memory.

A storage system, such as a solid-state drive (SSD), can include a memory controller and one or more memory devices, including a number of dies or logical units (LUNs). In certain examples, each die can include a number of memory arrays and peripheral circuitry thereon, such as die logic or a die processor. The memory controller can include interface circuitry configured to communicate with a host device (e.g., the host processor or interface circuitry) through a communication interface (e.g., a bidirectional parallel or serial communication interface). The memory controller can receive commands or operations from the host system in association with memory operations or instructions, such as read or write operations to transfer data (e.g., user data and associated integrity data, such as error data or address data, etc.) between the memory devices and the host device, erase operations to erase data from the memory devices, perform drive management operations (e.g., data migration, garbage collection (GC), block retirement), etc.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

FIG. 1 illustrates an example host system including a host device and a storage system.

FIG. 2 illustrates an example of an environment including a memory device.

FIG. 3A illustrates an example method for providing dynamic size of single level cell (SLC) static cache.

FIG. 3B illustrates an example table for providing dynamic size of SLC static cache.

FIG. 4 illustrates an example schematic diagram of a 3D NAND architecture semiconductor memory array.

FIG. 5 illustrates an example block diagram of a memory module.

FIG. 6 illustrates an example block diagram of an information handling system.

DETAILED DESCRIPTION

Software (e.g., programs), instructions, operating systems (OS), and other data are typically stored on storage systems and accessed by main memory for use by a host processor. Main memory (e.g., RAM) is typically faster, more expensive, and a different type of memory device (e.g., volatile) than a majority of the memory devices of the storage system (e.g., non-volatile, such as an SSD, etc.). In addition to the main memory, host systems can include different levels of volatile memory, such as a group of static memory (e.g., a cache, often SRAM), often faster than the main memory, in certain examples, configured to operate at speeds close to or exceeding the speed of the host processor, but with lower density and higher cost. In other examples, more or less levels or quantities of main memory or static memory can be used, depending on desired host system performance and cost.

Flash memory devices, such as SSD, typically include one or more groups of one-transistor, floating gate memory cells. Two common types of flash memory array architectures include NAND and NOR architectures. The floating gate memory cells of the memory array are typically arranged in a matrix. In some systems, partitions of memory can also be operated at different speeds by using a faster type of memory for certain partitions, making these advantages more pronounced. For example, a single-level cell memory (SLC) can be used instead of a triple-level cell memory (TLC) NAND, or 3D XPoint type memory can be used for designated partitions. The present subject matter can also be used for replacement gate memory cells. Other types of memory cells can be used without departing from the scope of the present subject matter.

Memory cells of a memory device can be arranged as either storing a single bit of data (SLC), or multiple bits of data (MLC). Types of MCL include triple-level cell (TLC) that can represent three bits of data per cell in one of 8 programmed states, and quad-level cell (QLC) that can represent four bits of data per cell in one of 16 programmed states. SLC memory cells typically offer the best performance and are more reliable. For example, SLC cells are written to with fewer programming cycles which reduces the chances of corruption from an unexpected power loss during programming. SLC cells however store less data and manufacturing memory devices in capacities suitable for use as a storage device using just SLC memory cells is less cost effective. A compromise solution that has been developed is to configure some cells as SLC and the rest of the cells as MLC. Data is first written to the SLC and then later transferred to the MLC when the memory device is not busy. In some examples, when receiving a host write request, the memory controller can first check to see if there is free SLC cache. If there is free SLC cache, the memory controller can write the data to the SLC cache. If there is no free SLC cache, the memory controller can directly write the data to MLC storage. The use of SLC cells in this way can be termed an SLC cache. This SLC cache mechanism provides a balance between the speed and reliability of SLC memory cells with the storage capacity of MLC memory cells.

In some example memory devices, the size of the SLC cache is fixed at device manufacturing time (fixed-size SLC cache). In other examples, since memory cells can be reconfigurable by firmware between SLC and MLC, the cache size can vary during usage (dynamic size SLC cache). In memory devices featuring dynamic size SLC caches, the cache size is typically varied based upon how full the memory device is (device utilization). As the device fills up, memory cells configured as SLC cache are migrated to MLC to increase total data storage capacity. Some example memory devices use dynamic size SLC cache based on the LS, but that SLC cache is dynamic SLC cache which means blocks can be used as SLC and TLC mode dynamically.

One downside to the use of SLC cache is that it increases the amount of times data is written to the physical memory because data is written twice—once to the SLC cache, and then later to MLC storage. Instances in which same data is written multiple times to flash is called Write Amplification (WA). WA can be defined as the actual amount of information physically written to the storage media in comparison to the logical amount intended to be written over the life of that data as it moves throughout the memory device. In addition to the use of SLC cache, an amount of WA is also affected by other necessary tasks on the NAND such as garbage collection. The larger the SLC cache, the more likely a write request is to be serviced by SLC cache. Consequentially, the larger the SLC cache the greater the likelihood of an increase in write amplification.

There are two types of SLC cache: static SLC cache in which blocks can only be used for in SLC mode; and dynamic SLC cache in which blocks can be used in SLC mode or TLC mode. Most current mobile storage devices use dynamic SLC cache. The maximum program/erase cycle (PEC) of the dynamic blocks is same as a TLC block regardless of whether the block is being used for SLC or TLC mode. Thus, for dynamic SLC cache, the tera bytes written (TBW) of a dynamic SLC block is limited to the TBW of a TLC block.

Currently, the static SLC cache size is fixed and the dynamic SLC cache size is dynamic. The present subject matter makes the static SLC cache size dynamically based on maximum logical saturation (LS) in a device lifetime, in various embodiments. For static SLC cache, the maximum PEC is 20-40 times of dynamic SLC cache, which means that static SLC cache may have 20-40 times data written in the same time period compared to the same size dynamic SLC cache.

An SLC block has only one third the capacity of a TLC block, since SLC is single bit of one cell and TLC is a triple bit of one cell. Because of the NAND character of the memory, the block should be erased before written (or programmed). When a host writes data to the device, the data will be programmed into the erased NAND blocks. Thus, the LS increases with the host writes to memory. As the host continues to write data after the LS reaches 100%, the device provides more space than the total capacity which is called over provisioning (OP). In addition, new writes make old data that has the same address with the new data invalid. Once the OP is consumed, the previously-written block is erased for the incoming data. Since the previous block has valid data, the valid data is moved to an erased block before being overwritten. This process is referred to as garbage collection (GC). In one example, if the OP is 7% of the device capacity, total device size is 107% of the device capacity. When the memory is full and LS is 100%, the average valid rate of the block is 100/107^(˜)=93%. Thus, a single block GC can use 7% free space of one block, such that to obtain one free block will use approximately 14 blocks of GC. If the OP increases, the number of blocks used for GC will drop, and the write performance will increase. Conversely, the write performance will drop significantly. In one example with 2.3% OP: 100/102.3^(˜)=97.7%, so about 43 blocks of GC are needed for one free block. The quantity of GC for 2.3% is almost 3 times of 7% OP which makes the write performance drop to ⅓. If all OP blocks are SLC, the OP will be ⅓ of all TLC blocks. What is needed is a method to obtain the TBW of static SLC cache without significant impact to overall write performance.

Each user of a device may use a different amount of memory over time. Thus, the maximum LS (MLS) over the lifetime of the memory or device may be different for different users of the same device type. In one example, the present subject matter provides for dynamically changing the static SLC cache size based on the MILS in the device life time. In this example, the memory controller monitors the MLS and then changes the static SLC cache size based on the MLS. According to one example, the present subject matter when MLS increases, the static SLC cache size is decreased. The decreased static SLC blocks are then used as dynamic SLC cache, which can be converted between SLC blocks and TLC blocks. Since dynamic SLC cache may have been used in TLC mode, the max PEC is reduced to the lower maximum PEC of the TLC blocks. Therefore, the dynamic SLC cache cannot be changed back to static SLC without causing a reliability issue.

In various embodiments, firmware for the memory controller recognizes two cache blocks pools: a static SLC blocks pool; and a dynamic blocks pool. When a memory block is included in the static SLC blocks pool, it will always be used as an SLC block. A memory block which is included in the dynamic blocks pool may be used as an SLC block or a TLC block. When a memory block is transferred from static SLC to dynamic, the memory block is moved from the SLC blocks pool to the dynamic blocks pool. However, the memory block cannot be subsequently moved from the dynamic blocks pool to the static SLC blocks pool, in various embodiments. When a memory block is in the static SLC blocks pool, it will be used as SLC cache. After the memory block is moved to the dynamic blocks pool, the memory block can be used as SLC cache or as a TLC block for non-cache data. Therefore, after reallocating a memory block from static to dynamic, static SLC cache size will be reduced but the total SLC cache size remains the same, and the OP will be increased which is a purpose of the reallocation in various embodiments.

The present subject matter provides apparatus and methods for providing dynamic size of static SLC cache. In one example, a method includes using a memory controller to track a maximum logical saturation over the lifespan of the memory device, where logical saturation is the percentage of capacity of the memory device written with data. A portion of a pool of memory cells of the memory device is reallocated from single level cell (SLC) static cache to SLC dynamic cache storage based at least in part on a value of the maximum logical saturation, the reallocating including writing at least one electrical state to a register, in some examples.

FIG. 1 illustrates an example system (e.g., a host system) 100 including a host device 105 and a storage system 110 configured to communicate over a communication interface (I/F) 115 (e.g., a bidirectional parallel or serial communication interface). The host device 105 can include a host processor 106 (e.g., a host central processing unit (CPU) or other processor or processing device) or other host circuitry (e.g., a memory management unit (MMU), interface circuitry, assessment circuitry 107, etc.). In certain examples, the host device 105 can include a main memory 108 (e.g., DRAM, etc.) and optionally, a static memory 109, to support operation of the host processor 106.

The storage system 110 can include a universal flash storage (UFS) device, an embedded MMC (eMMC™) device, or one or more other memory devices. For example, if the storage system 110 includes a UFS device, the communication interface 115 can include a serial bidirectional interface, such as defined in one or more Joint Electron Device Engineering Council (JEDEC) standards (e.g., JEDEC standard D223D (JESD223D), commonly referred to as JEDEC UFS Host Controller Interface (UFSHCI) 3.0, etc.). In another example, if the storage system 110 includes an eMMC device, the communication interface 115 can include a number of parallel bidirectional data lines (e.g., DAT[7:0]) and one or more command lines, such as defined in one or more JEDEC standards (e.g., JEDEC standard D84-B51 (JESD84-A51), commonly referred to as JEDEC eMMC standard 5.1, etc.). In other examples, the storage system 110 can include one or more other memory devices, or the communication interface 115 can include one or more other interfaces, depending on the host device 105 and the storage system 110.

The storage system 110 can include a memory controller 111, a random access memory (or cache) 113 and a non-volatile memory 112. In an example, the non-volatile memory can include a number of memory devices (e.g., dies or LUNs), such as one or more flash memory devices, etc., each including periphery circuitry thereon, and controlled by the memory controller 111.

Flash memory devices typically include one or more groups of one-transistor, floating gate memory cells. Two common types of flash memory array architectures include NAND and NOR architectures. The floating gate memory cells of the memory array are typically arranged in a matrix. The gates of each memory cell in a row of the array are coupled to an access line (e.g., a word line). In NOR architecture, the drains of each memory cell in a column of the array are coupled to a data line (e.g., a bit line). In NAND architecture, the drains of each memory cell in a column of the array are coupled together in series, source to drain, between a source line and a bit line.

Each memory cell in a NOR, NAND, 3D Cross Point (Xpoint), Holographic RAM (HRAM), MRAM, or one or more other architecture semiconductor memory array can be programmed individually or collectively to one or a number of programmed states. A single-level cell (SLC) can represent one bit of data per cell in one of two programmed states (e.g., 1 or 0). A multi-level cell (MLC) can represent two or more bits of data per cell in a number of programmed states (e.g., 2^(n), where n is the number of bits of data). In certain examples, MLC can refer to a memory cell that can store two bits of data in one of 4 programmed states. A triple-level cell (TLC) can represent three bits of data per cell in one of 8 programmed states. A quad-level cell (QLC) can represent four bits of data per cell in one of 16 programmed states. MLC is used herein in its broader context, to refer to any memory cell that can store more than one bit of data per cell (i.e., that can represent more than two programmed states), including TLC and QLC, etc.

The storage system 110 can include a multimedia card (MMC) solid-state storage device (e.g., micro secure digital (SD) cards, etc.). MMC devices include a number of parallel interfaces (e.g., an 8-bit parallel interface) with a host device 105, and are often removable and separate components from the host device. In contrast, embedded MMC (eMMC) devices are attached to a circuit board and considered a component of the host device, with read speeds that rival serial ATA (SATA) based SSD devices. As demand for mobile device performance continues to increase, such as to fully enable virtual or augmented-reality devices, utilize increasing networks speeds, etc., storage systems have shifted from parallel to serial communication interfaces. UFS devices, including controllers and firmware, communicate with a host device using a low-voltage differential signaling (LVDS) serial interface with dedicated read/write paths, further advancing read/write speeds between a host device and a storage system.

In three-dimensional (3D) architecture semiconductor memory device technology, vertical floating gate or charge trapping storage structures can be stacked, increasing the number of tiers, physical pages, and accordingly, the density of memory cells in a memory device.

Data is often stored arbitrarily on the storage system as small units. Even if accessed as a single unit, data can be received in small, random 4-16 k single file reads (e.g., 60%-80% of operations are smaller than 16 k). It is difficult for a user and even kernel applications to indicate that data should be stored as one sequential cohesive unit. File systems are typically designed to optimize space usage, and not sequential retrieval space.

The memory controller 111 can receive instructions from the host device 105, and can communicate with the non-volatile memory 112, such as to transfer data to (e.g., write or erase) or from (e.g., read) one or more of the memory cells of the non-volatile memory array 112. The memory controller 111 can include, among other things, circuitry or firmware, such as a number of components or integrated circuits. For example, the memory controller 111 can include one or more memory control units, circuits, or components configured to control access across the memory array and to provide a translation layer between the host device 105 and the storage system 100.

The non-volatile memory array 112 (e.g., a 3D NAND architecture semiconductor memory array) can include a number of memory cells arranged in, for example, a number of devices, planes, blocks, or physical pages. As one example, a TLC memory device can include 18,592 bytes (B) of data per page, 1536 pages per block, 548 blocks per plane, and 4 planes per device. As another example, an MLC memory device can include 18,592 bytes (B) of data per page, 1024 pages per block, 548 blocks per plane, and 4 planes per device, but with half the required write time and twice the program/erase (P/E) cycles as a corresponding TLC memory device. Other examples can include other numbers or arrangements.

Electronic devices, such as mobile electronic devices (e.g., smart phones, tablets, etc.), electronic devices for use in automotive applications (e.g., automotive sensors, control units, driver-assistance systems, passenger safety or comfort systems, etc.), and internet-connected appliances or devices (e.g., internet-of-things (IoT) devices, etc.), have varying storage needs depending on, among other things, the type of electronic device, use environment, performance expectations, etc.

Electronic devices can be broken down into several main components: a processor (e.g., a central processing unit (CPU) or other main processor); memory (e.g., one or more volatile or non-volatile random-access memory (RAM) memory device, such as dynamic RAM (DRAM), mobile or low-power double-data-rate synchronous DRAM (DDR SDRAM), etc.); and a storage device (e.g., non-volatile memory (NVM) device, such as flash memory, read-only memory (ROM), an SSD, an MMC, or other memory card structure or assembly, etc.). In certain examples, electronic devices can include a user interface (e.g., a display, touch-screen, keyboard, one or more buttons, etc.), a graphics processing unit (GPU), a power management circuit, a baseband processor or one or more transceiver circuits, etc.

FIG. 2 illustrates an example of an environment 200 including a host device 205 and a memory device 210 configured to communicate over a communication interface. The host device 205 or the memory device 210 can be included in a variety of products 250, such as Internet of Things (IoT) devices (e.g., a refrigerator or other appliance, sensor, motor or actuator, mobile communication device, automobile, drone, etc.) to support processing, communications, or control of the product 250.

The memory device 210 includes a memory controller 215 and a memory array 220 including, for example, a number of individual memory die (e.g., a stack of three-dimensional (3D) NAND die, one or more NAND dies, or the like). In 3D architecture semiconductor memory technology, vertical structures are stacked, increasing the number of tiers, physical pages, and accordingly, the density of a memory device (e.g., a storage device). In an example, the memory device 210 can be a discrete memory or storage device component of the host device 205. In other examples, the memory device 210 can be a portion of an integrated circuit (e.g., system on a chip (SOC), etc.), stacked or otherwise included with one or more other components of the host device 205.

One or more communication interfaces can be used to transfer data between the memory device 210 and one or more other components of the host device 205, such as a Serial Advanced Technology Attachment (SATA) interface, a Peripheral Component Interconnect Express (PCIe) interface, a Universal Serial Bus (USB) interface, a Universal Flash Storage (UFS) interface, an eMMC™ interface, or one or more other connectors or interfaces. The host device 205 can include a host system, an electronic device, a processor, a memory card reader, or one or more other electronic devices external to the memory device 210.

The memory controller 215 can be on one or more separate integrated circuits from the memory array 220 or can be on a same integrated circuit. In some examples, the functions of memory controller 215 can be divided across multiple integrated circuits. For example, some functionality can be on a separate integrated circuit and some functionality can be part of a controller on each memory die of the memory array 220. Memory controller 215 can receive instructions from the host 205, and can communicate with the memory array, such as to transfer data to (e.g., write or erase) or from (e.g., read) one or more of the memory cells, planes, sub-blocks, blocks, or pages of the memory array. The memory controller 215 can include, among other things, circuitry or firmware, including one or more components or integrated circuits. For example, the memory controller 215 can include one or more memory control units, circuits, or components configured to control access across the memory array 220 and to provide a translation layer between the host 205 and the memory device 210. The memory controller 215 can include one or more input/output (I/O) circuits, lines, or interfaces to transfer data to or from the memory array 220. The memory controller 215 can include a memory manager 225 and an array controller 235.

The memory manager 225 can include, among other things, circuitry or firmware, such as a number of components or integrated circuits associated with various memory management functions. For purposes of the present description example memory operation and management functions will be described in the context of NAND memory. Persons skilled in the art will recognize that other forms of non-volatile memory can have analogous memory operations or management functions. Such NAND management functions include wear leveling (e.g., garbage collection or reclamation), error detection or correction, block retirement, or one or more other memory management functions. The memory manager 225 can parse or format host commands (e.g., commands received from a host) into device commands (e.g., commands associated with operation of a memory array, etc.), or generate device commands (e.g., to accomplish various memory management functions) for the array controller 235 or one or more other components of the memory device 210.

The memory manager 225 can include a set of management tables 230 configured to maintain various information associated with one or more component of the memory device 210 (e.g., various information associated with a memory array or one or more memory cells coupled to the memory controller 215). For example, the management tables 230 can include information regarding block age, block erase count, error history, or one or more error counts (e.g., a write operation error count, a read bit error count, a read operation error count, an erase error count, etc.) for one or more blocks of memory cells coupled to the memory controller 215. In certain examples, if the number of detected errors for one or more of the error counts is above a threshold, the bit error can be referred to as an uncorrectable bit error. The management tables 230 can maintain a count of correctable or uncorrectable bit errors, among other things.

The array controller 235 can include, among other things, circuitry or components configured to control memory operations associated with writing data to, reading data from, or erasing one or more memory cells of the memory device 210 coupled to the memory controller 215. The memory operations can be based on, for example, host commands received from the host 205, or internally generated by the memory manager 225 (e.g., in association with wear leveling, error detection or correction, etc.).

The array controller 235 can include an error correction code (ECC) component 240, which can include, among other things, an ECC engine or other circuitry configured to detect or correct errors associated with writing data to or reading data from one or more memory cells of the memory device 210 coupled to the memory controller 215. The memory controller 215 can be configured to actively detect and recover from error occurrences (e.g., bit errors, operation errors, etc.) associated with various operations or storage of data, while maintaining integrity of the data transferred between the host 205 and the memory device 210, or maintaining integrity of stored data (e.g., using redundant RAID storage, etc.), and can remove (e.g., retire) failing memory resources (e.g., memory cells, memory arrays, pages, blocks, etc.) to prevent future errors.

In some examples, the memory array can comprise a number of NAND dies and one or more functions of the memory controller 215 for a particular NAND die can be implemented on an on-die controller on that particular die. Other organizations and delineations of control functionality can also be utilized, such as a controller for each die, plane, superblock, block, page, and the like.

The memory array 220 can include several memory cells arranged in, for example, a number of devices, semi-conductor dies, planes, sub-blocks, blocks, or pages. As one example, a 48 GB TLC NAND memory device can include 18,592 bytes (B) of data per page (16,384+2208 bytes), 1536 pages per block, 548 blocks per plane, and 4 or more planes per device. As another example, a 32 GB MLC memory device (storing two bits of data per cell (i.e., 4 programmable states)) can include 18,592 bytes (B) of data per page (16,384+2208 bytes), 1024 pages per block, 548 blocks per plane, and 4 planes per device, but with half the required write time and twice the program/erase (P/E) cycles as a corresponding TLC memory device. Other examples can include other numbers or arrangements. In some examples, a memory device, or a portion thereof, can be selectively operated in SLC mode, or in a desired MLC mode (such as TLC, QLC, etc.).

In operation, data is typically written to or read from the NAND memory device 210 in pages, and erased in blocks. However, one or more memory operations (e.g., read, write, erase, etc.) can be performed on larger or smaller groups of memory cells, as desired. The data transfer size of a NAND memory device 210 is typically referred to as a page, whereas the data transfer size of a host is typically referred to as a sector.

Although a page of data can include a number of bytes of user data (e.g., a data payload including a number of sectors of data) and its corresponding metadata, the size of the page often refers only to the number of bytes used to store the user data. As an example, a page of data having a page size of 4 KB can include 4 KB of user data (e.g., 8 sectors assuming a sector size of 512 B) as well as a number of bytes (e.g., 32 B, 54 B, 224 B, etc.) of metadata corresponding to the user data, such as integrity data (e.g., error detecting or correcting code data), address data (e.g., logical address data, etc.), or other metadata associated with the user data.

Different types of memory cells or memory arrays 220 can provide for different page sizes, or can require different amounts of metadata associated therewith. For example, different memory device types can have different bit error rates, which can lead to different amounts of metadata necessary to ensure integrity of the page of data (e.g., a memory device with a higher bit error rate can require more bytes of error correction code data than a memory device with a lower bit error rate). As an example, a multi-level cell (MLC) NAND flash device can have a higher bit error rate than a corresponding single-level cell (SLC) NAND flash device. As such, the MLC device can require more metadata bytes for error data than the corresponding SLC device.

FIG. 3A illustrates an example method 300 for providing dynamic size of single level cell (SLC) static cache. The method 300 includes, at a memory controller of a memory device having a lifespan: during operation of the memory device, tracking a maximum logical saturation over the lifespan of the memory device, where logical saturation is the percentage of capacity of the memory device written with data, at step 302. The method 300 further includes reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage based at least in part on a value of the maximum logical saturation, the reallocating including writing at least one electrical state to a register, at step 304.

FIG. 3B illustrates an example table for providing dynamic size of SLC static cache. In various embodiments, the device monitors the highest LS and changes the static SLC cache size based on the monitored highest LS. Thus, a memory device residing in different devices may have different static SLC cache sizes. In the depicted example, if the LS is A %, the SLC cache size is determined using the equation: (100%−A %)/3. In addition, assuming a current OP for the 100% LS is 7%, the OP static SLC cache is determined using the equation: ((100%−A %)/3+7%)/A %=(121−A)/(3A). As shown in the table of FIG. 3B, the largest number of blocks of GC to free one block is not increased. Thus, a device using the memory controller of the present subject matter can get the increased TBW benefit from the static SLC cache without increasing the worst-case GC to free additional storage.

In one example, a first user uses all the device total memory capacity, and then deletes some files before storing new files. Since the first user has used all the capacity of the device, the static SLC cache will be changed to dynamic cache using an equation or lookup table.

In another example, a second user controls usage by deleting some invalid files once the usage achieves a selected threshold. Because the second user has only used a small percentage of the capacity of the device, the static SLC cache will not be entirely converted to dynamic SLC cache of the device, and the second user can still get the benefit of very good write performance since the OP is more than 100%. In an example, the device can write all data to the static SLC cache which has approximately three times the write performance of TLC. In another example, the device moves the data in static SLC cache to TLC area during a specified time period.

FIG. 4 illustrates an example schematic diagram of a 3D NAND architecture semiconductor memory array 400 including a number of strings of memory cells (e.g., first-third A₀ memory strings 405A₀-407A₀, first-third A_(n) memory strings 405A_(n)-407A_(n), first-third B₀ memory strings 405B₀-407B₀, first-third B_(n) memory strings 405B_(n)-407B_(n), etc.), organized in blocks (e.g., block A 401A, block B 401B, etc.) and sub-blocks (e.g., sub-block A₀ 401A₀, sub-block A_(n) 401A_(n), sub-block B₀ 401B₀, sub-block B_(n) 401B_(n), etc.). The memory array 400 represents a portion of a greater number of similar structures that would typically be found in a block, device, or other unit of a memory device.

Each string of memory cells includes a number of tiers of charge storage transistors (e.g., floating gate transistors, charge-trapping structures, etc.) stacked in the Z direction, source to drain, between a source line (SRC) 435 or a source-side select gate (SGS) (e.g., first-third A₀ SGS 431A₀-433A₀, first-third A_(n) SGS 431A_(n)-433A_(n), first-third B₀ SGS 431B₀-433B₀, first-third B_(n) SGS 431B_(n)-433B_(n), etc.) and a drain-side select gate (SGD) (e.g., first-third A₀ SGD 426A₀-428A₀, first-third A_(n) SGD 426A_(n)-428A_(n), first-third B₀ SGD 426B₀-428B₀, first-third B_(n) SGD 426B_(n)-428B_(n), etc.). Each string of memory cells in the 3D memory array can be arranged along the X direction as data lines (e.g., bit lines (BL) BL0-BL6 420-422), and along the Y direction as physical pages.

Within a physical page, each tier represents a row of memory cells, and each string of memory cells represents a column. A sub-block can include one or more physical pages. A block can include a number of sub-blocks (or physical pages) (e.g., 128, 256, 384, etc.). Although illustrated herein as having two blocks, each block having two sub-blocks, each sub-block having a single physical page, each physical page having three strings of memory cells, and each string having 8 tiers of memory cells, in other examples, the memory array 400 can include more or fewer blocks, sub-blocks, physical pages, strings of memory cells, memory cells, or tiers. For example, each string of memory cells can include more or fewer tiers (e.g., 16, 32, 64, 128, etc.), as well as one or more additional tiers of semiconductor material above or below the charge storage transistors (e.g., select gates, data lines, etc.), as desired. As an example, a 48 GB TLC NAND memory device can include 18,592 bytes (B) of data per page (16,384+2208 bytes), 1536 pages per block, 548 blocks per plane, and 4 or more planes per device.

Each memory cell in the memory array 400 includes a control gate (CG) coupled to (e.g., electrically or otherwise operatively connected to) an access line (e.g., word lines (WL) WL0 ₀-WL7 ₀ 410A-417A, WL0 ₁-WL7 ₁ 410B-417B, etc.), which collectively couples the control gates (CGs) across a specific tier, or a portion of a tier, as desired. Specific tiers in the 3D memory array, and accordingly, specific memory cells in a string, can be accessed or controlled using respective access lines. Groups of select gates can be accessed using various select lines. For example, first-third A₀ SGD 426A₀-428A₀ can be accessed using an A₀ SGD line SGDA₀ 425A₀, first-third A_(n) SGD 426A_(n)-428A_(n) can be accessed using an SGD line SGDA_(n) 425A_(n), first-third B₀ SGD 426B₀-428B₀ can be accessed using an B₀ SGD line SGDB₀ 425B₀, and first-third B_(n) SGD 426B_(n)-428B_(n) can be accessed using an B_(n) SGD line SGDB_(n) 425B_(n). First-third A₀ SGS 431A₀-433A₀ and first-third A_(n) SGS 431A_(n)-433A_(n) can be accessed using a gate select line SGS₀ 430A, and first-third B₀ SGS 431B₀-433B₀ and first-third B_(n) SGS 431B_(n)-433B_(n) can be accessed using a gate select line SGS₁ 430B.

In an example, the memory array 400 can include a number of levels of semiconductor material (e.g., polysilicon, etc.) configured to couple the control gates (CGs) of each memory cell or select gate (or a portion of the CGs or select gates) of a respective tier of the array. Specific strings of memory cells in the array can be accessed, selected, or controlled using a combination of bit lines (BLs) and select gates, etc., and specific memory cells at one or more tiers in the specific strings can be accessed, selected, or controlled using one or more access lines (e.g., word lines).

In a NAND architecture semiconductor memory array, the state of a selected memory cell can be accessed by sensing a current or voltage variation associated with a particular data line containing the selected memory cell. The memory array 400 can be accessed (e.g., by a control circuit, one or more processors, digital logic, etc.) using one or more drivers. In an example, one or more drivers can activate a specific memory cell, or set of memory cells, by driving a particular potential to one or more data lines (e.g., bit lines BL0-BL2), access lines (e.g., word lines WL0-WL7), or select gates, depending on the type of operation desired to be performed on the specific memory cell or set of memory cells.

To program or write data to a memory cell, a programming voltage (Vpgm) (e.g., one or more programming pulses, etc.) can be applied to selected word lines (e.g., WL4 ₀), and thus, to a control gate of each memory cell coupled to the selected word lines. Programming pulses can begin, for example, at or near 15V, and, in certain examples, can increase in magnitude during each programming pulse application. While the program voltage is applied to the selected word lines, a potential, such as a ground potential (e.g., Vss), can be applied to the data lines (e.g., bit lines) and substrates (and thus the channels, between the sources and drains) of the memory cells targeted for programming, resulting in a charge transfer (e.g., direct injection or Fowler-Nordheim (FN) tunneling, etc.) from the channels to the floating gates of the targeted memory cells.

In contrast, a pass voltage (Vpass) can be applied to one or more word lines having memory cells that are not targeted for programming, or an inhibit voltage (e.g., Vcc) can be applied to data lines (e.g., bit lines) having memory cells that are not targeted for programming, for example, to inhibit charge from being transferred from the channels to the floating gates of such non-targeted memory cells. The pass voltage can be variable, depending, for example, on the proximity of the applied pass voltages to a word line targeted for programming. The inhibit voltage can include a supply voltage (Vcc), such as a voltage from an external source or supply (e.g., a battery, an AC-to-DC converter, etc.), relative to a ground potential (e.g., Vss).

As an example, if a programming voltage (e.g., 15V or more) is applied to a specific word line, such as WL4 ₀, a pass voltage of 10V can be applied to one or more other word lines, such as WL3 ₀, WL5 ₀, etc., to inhibit programming of non-targeted memory cells, or to retain the values stored on such memory cells not targeted for programming. As the distance between an applied program voltage and the non-targeted memory cells increases, the pass voltage required to refrain from programming the non-targeted memory cells can decrease. For example, where a programming voltage of 15V is applied to WL4 ₀, a pass voltage of 10V can be applied to WL3 ₀ and WL5 ₀, a pass voltage of 8V can be applied to WL2 ₀ and WL6 ₀, a pass voltage of 7V can be applied to WL1 ₀ and WL7 ₀, etc. In other examples, the pass voltages, or number of word lines, etc., can be higher or lower, or more or less.

Sense amplifiers can be coupled to one or more of the data lines (e.g., first, second, or third bit lines (BL0-BL2) 420-422), can detect the state of each memory cell in respective data lines by sensing a voltage or current on a particular data line.

Between applications of one or more programming pulses (e.g., Vpgm), a verify operation can be performed to determine if a selected memory cell has reached its intended programmed state. If the selected memory cell has reached its intended programmed state, it can be inhibited from further programming. If the selected memory cell has not reached its intended programmed state, additional programming pulses can be applied. If the selected memory cell has not reached its intended programmed state after a particular number of programming pulses (e.g., a maximum number), the selected memory cell, or a string, block, or page associated with such selected memory cell, can be marked as defective.

To erase a memory cell or a group of memory cells (e.g., erasure is typically performed in blocks or sub-blocks), an erasure voltage (Vers) (e.g., typically Vpgm) can be applied to the substrates (and thus the channels, between the sources and drains) of the memory cells targeted for erasure (e.g., using one or more bit lines, select gates, etc.), while the word lines of the targeted memory cells are kept at a potential, such as a ground potential (e.g., Vss), resulting in a charge transfer (e.g., direct injection or Fowler-Nordheim (FN) tunneling, etc.) from the floating gates of the targeted memory cells to the channels.

FIG. 5 illustrates an example block diagram of a memory device 500 including a memory array 502 having a plurality of memory cells 504, and one or more circuits or components to provide communication with, or perform one or more memory operations on, the memory array 502. Although shown with a single memory array 502, in other examples, one or more additional memory arrays, dies, or LUNs can be included herein. In certain examples, in a storage system having a number of dies or LUNs, the memory device 500 can represent a block diagram of circuits and components for each die or LUN. The memory device 500 can include a row decoder 512, a column decoder 514, sense amplifiers 520, a page buffer 522, a selector 524, an input/output (I/O) circuit 526, and a memory control unit 530.

The memory cells 504 of the memory array 502 can be arranged in blocks, such as first and second blocks 502A, 502B. Each block can include sub-blocks. For example, the first block 502A can include first and second sub-blocks 502A₀, 502A_(n), and the second block 502B can include first and second sub-blocks 502B₀, 502B_(n). Each sub-block can include a number of physical pages, each page including a number of memory cells 504. Although illustrated herein as having two blocks, each block having two sub-blocks, and each sub-block having a number of memory cells 504, in other examples, the memory array 502 can include more or fewer blocks, sub-blocks, memory cells, etc. In other examples, the memory cells 504 can be arranged in a number of rows, columns, pages, sub-blocks, blocks, etc., and accessed using, for example, access lines 506, first data lines 510, or one or more select gates, source lines, etc.

The memory control unit 530 can control memory operations of the memory device 500 according to one or more signals or instructions received on control lines 532, including, for example, one or more clock signals or control signals that indicate a desired operation (e.g., write, read, erase, etc.), or address signals (A0-AX) received on one or more address lines 516. One or more devices external to the memory device 500 can control the values of the control signals on the control lines 532, or the address signals on the address line 516. Examples of devices external to the memory device 500 can include, but are not limited to, a host, a memory controller, a processor, or one or more circuits or components not illustrated in FIG. 5 .

The memory device 500 can use access lines 506 and first data lines 510 to transfer data to (e.g., write or erase) or from (e.g., read) one or more of the memory cells 504. The row decoder 512 and the column decoder 514 can receive and decode the address signals (A0-AX) from the address line 516, can determine which of the memory cells 504 are to be accessed, and can provide signals to one or more of the access lines 506 (e.g., one or more of a plurality of word lines (WL0-WLm)) or the first data lines 510 (e.g., one or more of a plurality of bit lines (BL0-BLn)), such as described above.

The memory device 500 can include sense circuitry, such as the sense amplifiers 520, configured to determine the values of data on (e.g., read), or to determine the values of data to be written to, the memory cells 504 using the first data lines 510. For example, in a selected string of memory cells 504, one or more of the sense amplifiers 520 can read a logic level in the selected memory cell 504 in response to a read current flowing in the memory array 502 through the selected string to the data lines 510.

One or more devices external to the memory device 500 can communicate with the memory device 500 using the I/O lines (DQ0-DQN) 508, address lines 516 (A0-AX), or control lines 532. The input/output (I/O) circuit 526 can transfer values of data in or out of the memory device 500, such as in or out of the page buffer 522 or the memory array 502, using the I/O lines 508, according to, for example, the control lines 532 and address lines 516. The page buffer 522 can store data received from the one or more devices external to the memory device 500 before the data is programmed into relevant portions of the memory array 502, or can store data read from the memory array 502 before the data is transmitted to the one or more devices external to the memory device 500.

The column decoder 514 can receive and decode address signals (A0-AX) into one or more column select signals (CSEL1-CSELn). The selector 524 (e.g., a select circuit) can receive the column select signals (CSEL1-CSELn) and select data in the page buffer 522 representing values of data to be read from or to be programmed into memory cells 504. Selected data can be transferred between the page buffer 522 and the I/O circuit 526 using second data lines 518.

The memory control unit 530 can receive positive and negative supply signals, such as a supply voltage (Vcc) 534 and a negative supply (Vss) 536 (e.g., a ground potential), from an external source or supply (e.g., an internal or external battery, an AC-to-DC converter, etc.). In certain examples, the memory control unit 530 can include a regulator 528 to internally provide positive or negative supply signals.

FIG. 6 illustrates a block diagram of an example machine (e.g., a host system) 600 upon which any one or more of the techniques (e.g., methodologies) discussed herein may perform. In alternative embodiments, the machine 600 may operate as a standalone device or may be connected (e.g., networked) to other machines. In a networked deployment, the machine 600 may operate in the capacity of a server machine, a client machine, or both in server-client network environments. In an example, the machine 600 may act as a peer machine in peer-to-peer (P2P) (or other distributed) network environment. The machine 600 may be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile telephone, a web appliance, an IoT device, automotive system, or any machine capable of executing instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein, such as cloud computing, software as a service (SaaS), other computer cluster configurations.

Examples, as described herein, may include, or may operate by, logic, components, devices, packages, or mechanisms. Circuitry is a collection (e.g., set) of circuits implemented in tangible entities that include hardware (e.g., simple circuits, gates, logic, etc.). Circuitry membership may be flexible over time and underlying hardware variability. Circuitries include members that may, alone or in combination, perform specific tasks when operating. In an example, hardware of the circuitry may be immutably designed to carry out a specific operation (e.g., hardwired). In an example, the hardware of the circuitry may include variably connected physical components (e.g., execution units, transistors, simple circuits, etc.) including a computer-readable medium physically modified (e.g., magnetically, electrically, moveable placement of invariant massed particles, etc.) to encode instructions of the specific operation. In connecting the physical components, the underlying electrical properties of a hardware constituent are changed, for example, from an insulator to a conductor or vice versa. The instructions enable participating hardware (e.g., the execution units or a loading mechanism) to create members of the circuitry in hardware via the variable connections to carry out portions of the specific tasks when in operation. Accordingly, the computer-readable medium is communicatively coupled to the other components of the circuitry when the device is operating. In an example, any of the physical components may be used in more than one member of more than one circuitry. For example, under operation, execution units may be used in a first circuit of a first circuitry at one point in time and reused by a second circuit in the first circuitry, or by a third circuit in a second circuitry at a different time.

The machine (e.g., computer system, a host system, etc.) 600 may include a processing device 602 (e.g., a hardware processor, a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof, etc.), a main memory 604 (e.g., read-only memory (ROM), dynamic random-access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory 606 (e.g., static random-access memory (SRAM), etc.), and a storage system 618, some or all of which may communicate with each other via a communication interface (e.g., a bus) 630.

The processing device 602 can represent one or more general-purpose processing devices such as a microprocessor, a central processing unit, or the like. More particularly, the processing device can be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, or a processor implementing other instruction sets, or processors implementing a combination of instruction sets. The processing device 602 can also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. The processing device 602 can be configured to execute instructions 626 for performing the operations and steps discussed herein. The computer system 600 can further include a network interface device 608 to communicate over a network 620.

The storage system 618 can include a machine-readable storage medium (also known as a computer-readable medium) on which is stored one or more sets of instructions 626 or software embodying any one or more of the methodologies or functions described herein. The instructions 626 can also reside, completely or at least partially, within the main memory 604 or within the processing device 602 during execution thereof by the computer system 600, the main memory 604 and the processing device 602 also constituting machine-readable storage media.

The term “machine-readable storage medium” should be taken to include a single medium or multiple media that store the one or more sets of instructions, or any medium that is capable of storing or encoding a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present disclosure. The term “machine-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, optical media, and magnetic media. In an example, a massed machine-readable medium comprises a machine-readable medium with a plurality of particles having invariant (e.g., rest) mass. Accordingly, massed machine-readable media are not transitory propagating signals. Specific examples of massed machine-readable media may include: non-volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

The machine 600 may further include a display unit, an alphanumeric input device (e.g., a keyboard), and a user interface (UI) navigation device (e.g., a mouse). In an example, one or more of the display unit, the input device, or the UI navigation device may be a touch screen display. The machine a signal generation device (e.g., a speaker), or one or more sensors, such as a global positioning system (GPS) sensor, compass, accelerometer, or one or more other sensor. The machine 600 may include an output controller, such as a serial (e.g., universal serial bus (USB), parallel, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection to communicate or control one or more peripheral devices (e.g., a printer, card reader, etc.).

The instructions 626 (e.g., software, programs, an operating system (OS), etc.) or other data are stored on the storage system 618 can be accessed by the main memory 604 for use by the processing device 602. The main memory 604 (e.g., DRAM) is typically fast, but volatile, and thus a different type of storage than the storage system 618 (e.g., an SSD), which is suitable for long-term storage, including while in an “off” condition. The instructions 626 or data in use by a user or the machine 600 are typically loaded in the main memory 604 for use by the processing device 602. When the main memory 604 is full, virtual space from the storage system 618 can be allocated to supplement the main memory 604; however, because the storage system 618 device is typically slower than the main memory 604, and write speeds are typically at least twice as slow as read speeds, use of virtual memory can greatly reduce user experience due to storage system latency (in contrast to the main memory 604, e.g., DRAM). Further, use of the storage system 618 for virtual memory can greatly reduce the usable lifespan of the storage system 618.

The instructions 624 may further be transmitted or received over a network 620 using a transmission medium via the network interface device 608 utilizing any one of a number of transfer protocols (e.g., frame relay, internet protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), etc.). Example communication networks may include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), mobile telephone networks (e.g., cellular networks), Plain Old Telephone (POTS) networks, and wireless data networks (e.g., Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards known as Wi-Fi®, IEEE 802.16 family of standards known as WiMax®), IEEE 802.15.4 family of standards, peer-to-peer (P2P) networks, among others. In an example, the network interface device 608 may include one or more physical jacks (e.g., Ethernet, coaxial, or phone jacks) or one or more antennas to connect to the network 620. In an example, the network interface device 608 may include a plurality of antennas to wirelessly communicate using at least one of single-input multiple-output (SIMO), multiple-input multiple-output (MIMO), or multiple-input single-output (MISO) techniques. The term “transmission medium” shall be taken to include any intangible medium that is capable of storing, encoding, or carrying instructions for execution by the machine 600, and includes digital or analog communications signals or other intangible medium to facilitate communication of such software.

The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples”. Such examples can include elements in addition to those shown or described. However, the present inventor also contemplates examples in which only those elements shown or described are provided. Moreover, the present inventor also contemplates examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein”. Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

In various examples, the components, controllers, processors, units, engines, or tables described herein can include, among other things, physical circuitry or firmware stored on a physical device. As used herein, “processor” means any type of computational circuit such as, but not limited to, a microprocessor, a microcontroller, a graphics processor, a digital signal processor (DSP), or any other type of processor or processing circuit, including a group of processors or multi-core devices.

The term “horizontal” as used in this document is defined as a plane parallel to the conventional plane or surface of a substrate, such as that underlying a wafer or die, regardless of the actual orientation of the substrate at any point in time. The term “vertical” refers to a direction perpendicular to the horizontal as defined above. Prepositions, such as “on,” “over,” and “under” are defined with respect to the conventional plane or surface being on the top or exposed surface of the substrate, regardless of the orientation of the substrate; and while “on” is intended to suggest a direct contact of one structure relative to another structure which it lies “on” (in the absence of an express indication to the contrary); the terms “over” and “under” are expressly intended to identify a relative placement of structures (or layers, features, etc.), which expressly includes—but is not limited to—direct contact between the identified structures unless specifically identified as such. Similarly, the terms “over” and “under” are not limited to horizontal orientations, as a structure may be “over” a referenced structure if it is, at some point in time, an outermost portion of the construction under discussion, even if such structure extends vertically relative to the referenced structure, rather than in a horizontal orientation.

The terms “wafer” and “substrate” are used herein to refer generally to any structure on which integrated circuits are formed, and also to such structures during various stages of integrated circuit fabrication. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the various embodiments is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

Various embodiments according to the present disclosure and described herein include memory utilizing a vertical structure of memory cells (e.g., NAND strings of memory cells). As used herein, directional adjectives will be taken relative a surface of a substrate upon which the memory cells are formed (i.e., a vertical structure will be taken as extending away from the substrate surface, a bottom end of the vertical structure will be taken as the end nearest the substrate surface and a top end of the vertical structure will be taken as the end farthest from the substrate surface).

As used herein, directional adjectives, such as horizontal, vertical, normal, parallel, perpendicular, etc., can refer to relative orientations, and are not intended to require strict adherence to specific geometric properties, unless otherwise noted. For example, as used herein, a vertical structure need not be strictly perpendicular to a surface of a substrate, but may instead be generally perpendicular to the surface of the substrate, and may form an acute angle with the surface of the substrate (e.g., between 60 and 120 degrees, etc.).

In some embodiments described herein, different doping configurations may be applied to a select gate source (SGS), a control gate (CG), and a select gate drain (SGD), each of which, in this example, may be formed of or at least include polysilicon, with the result such that these tiers (e.g., polysilicon, etc.) may have different etch rates when exposed to an etching solution. For example, in a process of forming a monolithic pillar in a 3D semiconductor device, the SGS and the CG may form recesses, while the SGD may remain less recessed or even not recessed. These doping configurations may thus enable selective etching into the distinct tiers (e.g., SGS, CG, and SGD) in the 3D semiconductor device by using an etching solution (e.g., tetramethylammonium hydroxide (TMCH)).

Operating a memory cell, as used herein, includes reading from, writing to, or erasing the memory cell. The operation of placing a memory cell in an intended state is referred to herein as “programming,” and can include both writing to or erasing from the memory cell (i.e., the memory cell may be programmed to an erased state).

It will be understood that when an element is referred to as being “on,” “connected to” or “coupled with” another element, it can be directly on, connected, or coupled with the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled with” another element, there are no intervening elements or layers present. If two elements are shown in the drawings with a line connecting them, the two elements can be either be coupled, or directly coupled, unless otherwise indicated.

Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, the code can be tangibly stored on one or more volatile or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

Example 1 is a method comprising: at a memory controller of a memory device having a lifespan: during operation of the memory device, tracking a maximum logical saturation over the lifespan of the memory device, where logical saturation is the percentage of capacity of the memory device written with data; and reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage based at least in part on a value of the maximum logical saturation, the reallocating including writing at least one electrical state to a register.

In Example 2, the subject matter of Example 1 is optionally configured such that reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage includes using the logical saturation of the memory device as an input to a table stored in a memory of the memory device.

In Example 3, the subject matter of Example 1 or 2 is optionally configured such that tracking and reallocating are responsive to receiving a write request from a host.

In Example 4, the subject matter of any of Examples 1-3 is optionally configured such reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage includes providing SLC static cache size inversely proportional to the maximum logical saturation.

In Example 5, the subject matter of any of Examples 1-4 is optionally configured such that reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage includes providing SLC static cache size equal to (100−MLS)/3, where MILS is the maximum logical saturation.

In Example 6, the subject matter of any of Examples 1-5 is optionally configured such that reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage does not change combined SLC cache size.

In Example 7, the subject matter of any of Examples 1-6 is optionally configured such that a maximum program/erase cycle (PEC) of SLC static cache is 20 to 40 times greater than a maximum PEC of SLC dynamic cache.

Example 8 is a memory device comprising: a memory controller configured to perform operations during operation of the memory device comprising: tracking a maximum logical saturation over the lifespan of the memory device, where logical saturation is the percentage of capacity of the memory device written with data; and reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage based at least in part on a value of the maximum logical saturation, the reallocating including writing at least one electrical state to a register.

In Example 9, the subject matter of Example 8 is optionally configured such that the SLC dynamic storage is configured to be used for an SLC storage mode or a multi-level cell (MLC) storage mode.

In Example 10, the subject matter of Example 9 is optionally configured such that, in MLC storage mode, a memory cell stores three or more bits of data per memory cell.

In Example 11, the subject matter of any of Examples 8-10 is optionally configured such that reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage includes using the logical saturation of the memory device as an input to a table stored in a memory of the memory device.

In Example 12, the subject matter of any of Examples 8-11 is optionally configured such that at least one of tracking and reallocating are responsive to receiving a write request from a host.

In Example 13, the subject matter of any of Examples 8-11 is optionally configured such that at least one of tracking and reallocating are performed periodically.

In Example 14, the subject matter of any of Examples 8-11 is optionally configured such that at least one of tracking and reallocating are performed on a programmable schedule.

Example 15 is a machine-readable medium, storing instructions, when performed by a controller of a memory device, cause the controller to perform operations during operation of the memory device comprising: tracking a maximum logical saturation over the lifespan of the memory device, where logical saturation is the percentage of capacity of the memory device written with data; and reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage based at least in part on a value of the maximum logical saturation, the reallocating including writing at least one electrical state to a register.

In Example 16, the subject matter of Example 15 is optionally configured such that reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage includes providing SLC static cache size inversely proportional to the maximum logical saturation.

In Example 17, the subject matter of Example 15 or 16 is optionally configured such reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage includes providing SLC static cache size equal to (100−MLS)/3, where MLS is the maximum logical saturation.

In Example 18, the subject matter of any of Examples 15-17 is optionally configured such that reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage does not change combined SLC cache size.

In Example 19, the subject matter of any of Examples 15-18 is optionally configured such that a maximum program/erase cycle (PEC) of SLC static cache is 20 to 40 times greater than a maximum PEC of SLC dynamic cache.

In Example 20, the subject matter of any of Examples 15-19 is optionally configured such that reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage includes using the logical saturation of the memory device as an input to a table stored in a memory of the memory device.

Example 21 is at least one machine-readable medium including instructions that, when executed by processing circuitry, cause the processing circuitry to perform operations to implement of any of Examples 1-20.

Example 22 is an apparatus comprising means to implement of any of Examples 1-20.

Example 23 is a system to implement of any of Examples 1-20.

Example 24 is a method to implement of any of Examples 1-20.

The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. 

What is claimed is:
 1. A storage system comprising: a memory device including single level cell (SLC) static cache memory cells and SLC dynamic cache memory cells; and a memory controller configured to perform operations comprising: tracking a maximum logical saturation over a lifespan of the memory device, where logical saturation is the percentage of a capacity of the memory device written with data at a particular time during the lifespan of the memory device; using the tracked logical saturation as an input to a table stored in the memory device; and determining a portion of a pool of memory cells of the memory device to be reallocated from single level cell (SLC) static cache memory cells to SLC dynamic cache memory cells using the table and based on a current value of the maximum logical saturation, the reallocating including writing at least one electrical state to a register, wherein the capacity of the memory device is variable based on the reallocating.
 2. The storage system of claim 1, wherein the SLC dynamic storage is configured to be used for an SLC storage mode or a multi-level cell (MLC) storage mode.
 3. The storage system of claim 2, wherein, in MLC storage mode, a memory cell stores three or more bits of data per memory cell.
 4. The storage system of claim 1, wherein reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage includes providing SLC static cache size inversely proportional to the maximum logical saturation.
 5. The storage system of claim 1, wherein at least one of tracking and reallocating are responsive to receiving a write request from a host.
 6. The storage system of claim 1, wherein at least one of tracking and reallocating are performed periodically.
 7. The storage system of claim 1, wherein at least one of tracking and reallocating are performed on a programmable schedule.
 8. A method comprising: at a memory controller of a memory device having a lifespan: during operation of the memory device, tracking a maximum logical saturation over the lifespan of the memory device, where logical saturation is the percentage of a capacity of the memory device written with data at a particular time during the lifespan of the memory device; using the tracked logical saturation as an input to a table stored in the memory device; and determining a portion of a pool of memory cells of the memory device to be reallocated from single level cell (SLC) static cache memory cells to SLC dynamic cache memory cells using the table and based on a current value of the maximum logical saturation, the reallocating including writing at least one electrical state to a register, wherein the capacity of the memory device is variable based on the reallocating.
 9. The method of claim 8, wherein tracking and reallocating are responsive to receiving a write request from a host.
 10. The method of claim 8, wherein at least one of tracking and reallocating are performed periodically.
 11. The method of claim 8, wherein at least one of tracking and reallocating are performed on a programmable schedule.
 12. The method of claim 8, wherein reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage includes providing SLC static cache size inversely proportional to the maximum logical saturation.
 13. The method of claim 8, wherein reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage does not change combined SLC cache size.
 14. The method of claim 8, wherein a maximum program/erase cycle (PEC) of SLC static cache is 20 to 40 times greater than a maximum PEC of SLC dynamic cache.
 15. A machine-readable medium, storing instructions, when performed by a controller of a memory device, cause the controller to perform operations during operation of the memory device comprising: tracking a maximum logical saturation over a lifespan of the memory device, where logical saturation is the percentage of a capacity of the memory device written with data at a particular time during the lifespan of the memory device; using the tracked logical saturation as an input to a table stored in the memory device; and determining a portion of a pool of memory cells of the memory device to be reallocated from single level cell (SLC) static cache memory cells to SLC dynamic cache memory cells using the table and based on a current value of the maximum logical saturation, the reallocating including writing at least one electrical state to a register, wherein the capacity of the memory device is variable based on the reallocating.
 16. The machine-readable medium of claim 15, wherein reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage includes providing SLC static cache size inversely proportional to the maximum logical saturation.
 17. The machine-readable medium of claim 15, wherein reallocating a portion of a pool of memory cells of the memory device from single level cell (SLC) static cache to SLC dynamic cache storage does not change combined SLC cache size.
 18. The machine-readable medium of claim 15, wherein a maximum program/erase cycle (PEC) of SLC static cache is 20 to 40 times greater than a maximum PEC of SLC dynamic cache.
 19. The machine-readable medium of claim 15, wherein at least one of tracking and reallocating are performed periodically.
 20. The machine-readable medium of claim 15, wherein at least one of tracking and reallocating are performed on a programmable schedule. 